Figure 3

(a), Scattering loss (α_s) of TE-polarized modes in waveguides designed for Cherenkov phase-matching with 98 nm thick SiN, a sidewall roughness σ_side = 7 nm RMS, and a top surface roughness σ_surface = 0.25 nm RMS. The absorption loss α_a is calculated from the material absorption loss of SiN scaled by the confinement factor, where α_SiN = 14 dB/cm. Measured propagation losses for the BBO/SiN and the air-clad SiN waveguides are plotted with data points, and error bars indicate the standard deviations of the measurement uncertainties. (b), Normalized conversion efficiency for SHG simulated across a broad range of pump wavelengths, plotted in blue on the left axis. The corresponding Cherenkov angle is plotted in orange on the right axis. Solid lines represent a waveguide with a 100 nm height and a 1500 nm width, which is the geometry optimized for SHG from a 445 nm wavelength pump. Dashed lines represent a waveguide with a 96 nm height and a 2000 nm width, showcasing a finite frequency conversion across the entire pump wavelength range of 400–1000 nm.